Radiation-sensitive silver chloride containing photographic emulsions are known to offer specific advantages. For example, silver chloride exhibits less native sensitivity to the visible portion of the spectrum than other photographically useful silver halides. Further, silver chloride is more soluble than other photographically useful silver halides, thereby permitting development and fixing to be achieved in shorter times.
It is well recognized in the art that silver chloride strongly favors the formation of crystals having {100} crystal faces. In the overwhelming majority of photographic emulsions silver chloride crystals when present are in the form of cubic grains. With some difficulty it has been possible to modify the crystal habit of silver chloride. Claes et al, "Crystal Habit Modification of AgCl by Impurities Determining Solvation", The Journal of Photographic Science, Vol. 21, pp. 39-50, 1973, teaches the formation of silver chloride crystals with {110} and {111} faces through the use of various grain growth modifiers. Wyrsch, "Sulfur Sensitization of Monosized Silver Chloride Emulsions with {111}, {110}, and {100} Crystal Habit", Paper III-13, International Congress of Photographic Science, pp. 122-124, 1978, discloses a triple-jet precipitation process in which silver chloride is precipitated in the presence of ammonia and small amounts of divalent cadmium ions. In the presence of cadmium ions control of pAg (the negative logrithim of silver ion concentration) and pH resulted in the formation of rhombododecahedral, octahedral, and cubic crystal habits, presenting grain faces lying in {110}, {111}, and {100} crystallographic planes, respectively.
Tabular silver bromide grains have been extensively studied, often in macro-sizes having no photographic utility. Tabular grains are herein defined as those having two substantially parallel crystal faces, each of which is substantially larger than any other single crystal face of the grain. The aspect ratio--that is, the ratio of diameter to thickness--of tabular grains is substantially greater than 1:1. High aspect ratio tabular grain silver bromide emulsions were reported by deCugnac and Chateau, "Evolution of the Morphology of Silver Bromide Crystals During Physical Ripening", Science et Industries Photographiques, Vol. 33, No. 2 (1962), pp. 121-125.
From 1937 until the 1950's the Eastman Kodak Company sold a Duplitized.RTM. radiographic film product under the name No-Screen X-Ray Code 5133. The product contained as coatings on opposite major faces of a film support sulfur sensitized silver bromide emulsions. Since the emulsions were intended to be exposed by X-radiation, they were not spectrally sensitized. The tabular grains had an average aspect ratio in the range of from about 5 to 7:1. The tabular grains accounted for greater than 50% of the projected area while nontabular grains accounted for greater than 25% of the projected area. The emulsion having the highest average aspect ratio, chosen from several remakes, had an average tabular grain diameter of 2.5 microns, an average tabular grain thickness of 0.36 micron, and an average aspect ratio of 7:1. In other remakes the emulsions contained thicker, smaller diameter tabular grains which were of lower average aspect ratio.
Although tabular grain silver bromoiodide emulsions are known in the art, none exhibit a high average aspect ratio. A discussion of tabular silver bromoiodide grains appears in Duffin, Photographic Emulsion Chemistry, Focal Press, 1966, pp. 66-72, and Trivelli and Smith, "The Effect of Silver Iodide Upon the Structure of Bromo-Iodide Precipitation Series", The Photographic Journal, Vol. LXXX, July 1940, pp. 285-288. Trivelli and Smith observed a pronounced reduction in both grain size and aspect ratio with the introduction of iodide. Gutoff, "Nucleation and Growth Rates During the Precipitation of Silver Halide Photographic Emulsions", Photographic Sciences and Engineering, Vol. 14, No. 4, July-August 1970, pp. 248-257, reports preparing silver bromide and silver bromoiodide emulsions of the type prepared by single-jet precipitations using a continuous precipitation apparatus.
Bogg, Lewis, and Maternaghan have recently published specific processes of preparing silver halide emulsions in which the grains are tabular--that is areally extended as compared to their thickness. Bogg U.S. Pat. No. 4,063,951 teaches forming silver halide crystals of tabular habit bounded by {100} cubic faces and having an aspect ratio (here the ratio of edge length to thickness) of from 1.5 to 7:1 by a double-jet precipitation technique in which pAg is controlled within the range of from 5.0 to 7.0. As shown in FIG. 3 of Bogg, the silver halide grains formed exhibit square and rectangular major surfaces characteristic of {100} crystal faces. Lewis U.S. Pat. No. 4,067,739 teaches the preparation of monosize silver halide emulsions wherein most of the crystals are of the twinned octahedral type by forming seed crystals, causing the seed crystals to increase in size by Ostwald ripening in the presence of a silver halide solvent, and completing grain growth without renucleation or Ostwald ripening while controlling pBr (the negative logarithm of bromide ion concentration). Lewis does not mention silver chloride. Maternaghan U.S. Pat. Nos. 4,150,994, 4,184,877, and 4,184,878, U.K. Pat. No. 1,570,581, and German OLS publications Nos. 2,905,655 and 2,921,077 teach the formation of silver halide grains of flat twinned octahedral configuration by employing seed crystals which are at least 90 mole percent iodide. (Except as otherwise indicated, all references to halide percentages are based on silver present in the corresponding emulsion, grain, or grain region being discussed; e.g., a grain consisting of silver chlorobromide containing 60 mole percent chloride also contains 40 mole percent bromide.)
Wey, IMPROVED DOUBLE-JET PRECIPITATION PROCESSES AND PRODUCTS THEREOF, U.S. Ser. No. 429,403, filed concurrently herewith and commonly assigned, which is a continuation-in-part of U.S. Ser. No. 320,908, filed Nov. 12, 1981, now abandoned, discloses the preparation of tabular silver chloride grains which are substantially internally free of bromide and iodide. A higher proportion of nontabular grains and lower grain sizes are produced when tabular grain nucleation is undertaken in the presence of iodide. The tabular silver chloride grains are the products of an ammoniacal double-jet precipitation process. The tabular grains produced appear to have substantially parallel major crystals faces of primarily truncated triangular (typically irregular hexagonal) configuration. Both the major faces and the edges of the grains appear to lie entirely within {111} crystallographic planes. The average aspect ratio of the tabular grains is above 8:1.
E. Klein and E. Moisar, Berichte der Bungesellschaft, 67 (4), 349-355, 1963, reports an inhibiting effect upon the grain growth of silver chloride when purine bases, such as adenine, are added at various stages of emulsion precipitation. Halwig U.S. Pat. No. 3,519,426 discloses the preparation of silver chloride emulsions of increased covering power by precipitating in the presence of an azaindene, such as a tetraazaindene, pentaazaindene, or adenine. It is, of course, recognized that the covering power of silver halide emulsions of finer grain size is greater than that of silver halide emulsions of larger grain size, other features being comparable.
It is known in the art that silver halide grains can be precipitated in the presence of a variety of peptizers. Smith et al U.S. Pat. No. 3,415,653 discloses the precipitation of silver bromoiodide grains of a variety of shapes, including tabular, by employing a copolymer of vinylamine and acrylic acid as a peptizer. Smith et al U.S. Pat. No. 3,692,753 uses as a peptizer which can be coagulated and redispersed an interpolymer of at least three different monomers, one of which is an acrylamide or acrylate containing an appended alkyl chain containing one or two sulfur atoms substituted for linking alkyl carbons. Smith et al U.S. Pat. No. 3,615,624 discloses for use in peptizing silver chloride, a linear copolymer having recurring units of amides or esters of maleic, acrylic, or methacrylic acid in which the amine or alcohol condensation residue contains an organic radical having at least one sulfur atom linking two alkyl carbon atoms. In one investigation of neutral silver bromoiodide emulsions precipitated similarly to Example 5 of Smith et al U.S. Pat. No. 3,615,624 an emulsion was observed in which less than 20 percent of the projected area of the silver bromoiodide grains was accounted for by tabular grains. The tabular grains, though of low aspect ratio, appeared to have peripheral edges lying parallel to &lt;211&gt; crystallographic vectors lying in the plane of the major faces.
Wilgus and Haefner U.S. Ser. No. 429,420, filed concurrently herewith and commonly assigned, titled HIGH ASPECT RATIO SILVER BROMOIODIDE EMULSIONS AND PROCESSES FOR THEIR PREPARATION, which is a continuation-in-part of U.S. Ser. No. 320,905, filed Nov. 12, 1981, now abandoned, discloses high aspect ratio silver bromoiodide emulsions and a process for their preparation.
Kofron et al U.S. Ser. No. 429,407, filed concurrently herewith and commonly assigned, titled SENSITIZED HIGH ASPECT RATIO SILVER HALIDE EMULSIONS AND PHOTOGRAPHIC ELEMENTS, which is a continuation-in-part of U.S. Ser. No. 320,904, filed Nov. 12, 1981, now abandoned, discloses chemically and spectrally sensitized high aspect ratio tabular grain silver halide emulsions and photographic elements incorporating these emulsions.
Daubendiek and Strong U.S. Ser. No. 429,587, filed concurrently herewith and commonly assigned, titled AN IMPROVED PROCESS FOR THE PREPARATION OF HIGH ASPECT RATIO SILVER BROMOIODIDE EMULSIONS, which is a continuation-in-part of U.S. Ser. No. 320,906, filed Nov. 12, 1981, now abandoned, discloses an improvement on the processes of Maternaghan whereby high aspect ratio tabular grain silver bromoiodide emulsions can be prepared.
Abbott and Jones U.S. Ser. No. 430,222, filed concurrently herewith and commonly assigned, titled RADIOGRAPHIC ELEMENTS EXHIBITING REDUCED CROSSOVER, which is a continuation-in-part of U.S. Ser. No. 320,907, filed Nov. 12, 1981, now abandoned, discloses the use of high aspect ratio tabular grain silver halide emulsions in radiographic elements coated on both major surfaces of a radiation transmitting support to control crossover.
Solberg, Piggin, and Wilgus U.S. Ser. No. 431,913, filed concurrently herewith and commonly assigned, titled RADIATION-SENSITIVE SILVER BROMOIODIDE EMULSIONS, PHOTOGRAPHIC ELEMENTS, AND PROCESSES FOR THEIR USE, which is a continuation-in-part of U.S. Ser. No. 320,909, filed Nov. 12, 1981, now abandoned discloses high aspect ratio tabular grain silver bromoiodide emulsions wherein a higher concentration of iodide is present in an annular region than in a central region of the tabular grains.
Mignot U.S. Ser. No. 320,912, filed Nov. 12, 1981 and commonly assigned, titled SILVER BROMIDE EMULSIONS OF NARROW GRAIN SIZE DISTRIBUTION AND PROCESSES FOR THEIR PREPARATION discloses high aspect ratio tabular grain silver bromide emulsions wherein the tabular grains are square or rectangular in projected area.
Dickerson U.S. Ser. No. 430,574, filed concurrently herewith and commonly assigned, titled FOREHARDENED PHOTOGRAPHIC ELEMENTS AND PROCESSES FOR THEIR USE, which is a continuation-in-part of U.S. Ser. No. 320,910, filed Nov. 12, 1981, now abandoned discloses producing silver images of high covering power by employing photographic elements containing forehardened high aspect ratio tabular grain silver halide emulsions.
Jones and Hill U.S. Ser. No. 430,092, filed concurrently herewith and commonly assigned, titled PHOTOGRAPHIC IMAGE TRANSFER FILM UNIT, which is a continuation-in-part of U.S. Ser. No. 320,911, filed Nov. 12, 1981, now abandoned, discloses image transfer film units containing tabular grain silver halide emulsions.
Evans et al U.S. Ser. No. 431,912, filed concurrently herewith and commonly assigned, titled DIRECT REVERSAL EMULSIONS AND PHOTOGRAPHIC ELEMENTS USEFUL IN IMAGE TRANSFER FILMS which is a continuation-in-part of U.S. Ser. No. 320,891, filed Nov. 12, 1981, now abandoned, discloses image transfer film units containing tabular grain core-shell silver halide emulsions.